The technical module (TM) of the DVB (Digital Video Broadcast) committee is investigating the definition of a second-generation system for satellite broadcasting (DVB-S2) in order to increase the bit rate and the power efficiency in future satellite broadcast systems. Two main approaches for coding and modulation are considered. The first one is totally incompatible with the current DVB-S (Digital Video Broadcasting for Satellite) standard including e.g. turbo coding with high spectral efficient modulations, while the second one is backward compatible.
The article by A. Morello and V. Mignone, entitled “Backward compatible solutions for DVB-S2”, DVB Technical module, TM2638, describes a backward compatible system with which additional data rate can be provided by using the hierarchical Non-Uniform 8-PSK (8 states—Phase Shift Keying) modulation instead of the classical QPSK (Quadrature Phase Shift Keying) modulation. A problem of such a system using the hierarchical non-uniform 8-PSK modulation is that the angle between the symbols in the non-uniform 8-PSK signal constellation must be kept rather small (<π/8) because this angle deviation introduced by the hierarchical constellation will be considered as an additional noise factor by the classical QPSK demodulator at the receiver side. Hence, the minimum distance of the non-uniform constellation stays rather small. Consequently, the additional data must be protected with a powerful and low-rate channel coding scheme. This necessitates a rather complex algorithm to decode the additional data.